The present invention relates in general to an apparatus and method for laying wire, and in particular but not exclusively to a tool for laying wire into the surface of a body. In a preferred embodiment, the invention relates to a method and apparatus for laying wire into an interior bore-surface of a pipe fitting.
Pipe fittings are commonly used to couple the ends of pipes including, for example, plastics material gas supply pipes. Such pipes must be connected by a sealed joint so that, in use, no gas is permitted to escape through the joint.
One known method of making such a sealed joint is to engage the ends of the plastic pipes to be joined in a pipe fitting in the form of a cylindrical sleeve. An electrical conductor is embedded in an inner bore-surface of the sleeve, usually in the form of a helical coil of copper wire. When an end of each pipe is positioned in the sleeve, an electrical current is passed through the wire causing the wire to become heated, thereby melting the plastics material on the bore-surface of the sleeve or on the exterior surfaces of the pipes, or both. The end of the pipe thereby becomes fused or welded to the sleeve in a gas-tight sealed joint.
EP-A-0,569,625 discloses a prior art apparatus for laying wire into the interior bore surface of a pipe fitting, comprising a cutting tool for cutting a groove in the interior surface, a wire guide for guiding wire into the groove, and an enclosing means for returning the cut material back into the groove to enclose the wire.
A problem arises with the prior art apparatus and method in that a separate tool is required for each diameter of pipe fitting, because the shape of the prior art tool closely follows the internal diameter of the pipe fitting. When the wire laying tool is used on an inappropriate size of sleeve, the wire is not correctly laid into the groove and instead tends to run free inside the fitting, rendering the fitting useless.
It is desired to improve the flexibility and reliability of the prior art method and apparatus. Also, in at least a first preferred embodiment, it is desired to provide a method and apparatus for laying wire into a body having a non-constant internal diameter. That is, an internal diameter that varies along all or part of the length of the body, such as a reducer pipe fitting.
Further, it is desired to provide a method and apparatus for laying wire into a body having a non-useable area, such as a side aperture of a T-shaped pipe fitting. It is desired to lay a single wire along a T-shaped pipe fitting in a helical coil at and near first and second ends thereof but avoiding the side aperture.
Further still, in another preferred embodiment, it is desired to provide an improved method and apparatus for laying a double helical coil of a single piece of wire such that the wire returns to near a starting point.
According the a first aspect of the present invention there is provided a wirelaying apparatus for laying wire into an interior bore surface of a hollow cylinder, comprising: cutting means for making a cut into said interior bore surface; wire guide means for guiding wire into the cut; and enclosing means for closing the cut thereby enclosing the wire in the cut; characterised in that: said wire guide means is arranged such that the wire enters the cut through the cutting means.
Advantageously, the wire enters the cut directly through the cutting means and therefore cannot run free.
Preferably, the wire is guided through an aperture in the cutting means ideally to an exterior surface of the cutting means that, in use, faces into the cut.
Preferably, the cutting means is arranged to produce a cut which is substantially normal to said interior bore surface, and in the form of a groove, with said cutting means preferably lifting a flange to one side of the cut. Ideally, the guide means guides the wire into the cut to an area underneath the flange, and preferably a corner position underneath the flange.
Preferably, said wirelaying apparatus comprises a wirelaying tool integrally forming said cutting means, said wire guide means and said enclosing means. Preferably, said tool is arranged to be carried on an elongate bar, with said wire preferably being fed along the bar, suitably by a wire delivery means such as pulley arrangement, to said wire guide means.
The preferred embodiment is particularly intended for laying wire into the interior bore surface of a plastics material pipe or pipe fitting. Said wirelaying apparatus is preferably arranged to receive said pipe or pipe fitting for rotation about a longitudinal axis thereof with said wirelaying tool being held on said bar against said interior bore surface such that the pipe fitting is operatively rotated with respect to the wirelaying tool.
Preferably, the wirelaying tool is arranged such that said enclosing means is in a plane normal to the longitudinal rotational axis of the pipe fitting. Therefore, maximum pressure may be applied by the enclosing means to close the flap cut by the cutting means even if the tool is used with a pipe fitting having an internal diameter substantially greater than the exterior circumference of the tool. However, the wirelaying tool is preferably arranged to have an exterior circumference corresponding to the interior diameter of an intended pipe fitting.
Preferably, the wirelaying tool is mounted into a receiving recess in said bar such that said tool is carried aligned with an end face and an outer circumferential face of the bar. By mounting the wirelaying tool in this position on the bar, several operational advantages are achieved. In particular, the cutting means is arranged to lie at or near the end of the bar. Placing the cutting tool in this position allows the cutting tool to remain in contact with the interior bore surface even if the internal diameter of the bore surface changes along the length of the pipe fitting, such as in a reducer used to couple pipes of different diameters.
A further advantage of the wirelaying apparatus is that the pitch of the helical path followed by the wirelaying tool may -be changed during wirelaying. In particular, the wirelaying apparatus may move the wirelaying tool to greatly increase the pitch of the helical path. This feature is particularly advantageous, for example, in laying a continuous piece of wire within a T-shaped pipe fitting such that the wire may be laid to avoid a side aperture of the T-shaped fitting.
According to a second aspect of the present invention there is provided a wirelaying apparatus, for laying wire into a body, said apparatus comprising a cutting means that is rotatable about an axis substantially normal to an interior bore surface of said body.
The cutting means is preferably provided with a cutting face preferably intended for making a cut, in use, by moving said cutting means through said interior bore surface, in the direction of said cutting face. Advantageously, said cutting means is rotatable, such that said cutting face is rotated about said axis. Preferably, a wire guide means guides a wire through said cutting means along said axis such that said cutting means rotates about said wire.
Advantageously, the cutting tool is driven in a first direction, to lay wire in a first helical path, is then rotated through substantially 20xc2x0 and driven to lay wire along a linear path, and then rotated through a further 90xc2x0, to lay wire in a second helical path. Preferably, the second helical path lies between said first helical path such that a double helical path is formed.